WO2018014136A1

WO2018014136A1 - Process for recycling graphene from an electrode material

Info

Publication number: WO2018014136A1
Application number: PCT/CA2017/050880
Authority: WO
Inventors: Nicolas DELAPORTE; Diby Benjamin OSSONON; Karim Zaghib; Daniel Belanger
Original assignee: HYDRO-QUéBEC; Transfert Plus, S.E.C.
Priority date: 2016-07-22
Filing date: 2017-07-21
Publication date: 2018-01-25
Also published as: EP3488486A4; EP3488486B1; US10811736B2; US20190288349A1; CA3031449A1; EP3488486A1; JP2019523528A; JP6983220B2; ES2876436T3; CA3031449C; CN109792095B; CN109792095A; KR102464316B1; KR20190038853A

Abstract

A process for recycling an electrode material comprising graphene and an electrochemically active material is described. The process comprises a step of adding, in any order, water and an immiscible solvent to the electrode material, thus forming a two-phase system comprising an organic phase and an aqueous phase; and a step of separating and filtering the organic phase in order to recover the graphene. The process optionally comprises additional washing, drying and/or heat treatment steps. The electrodes comprising the recycled graphene, as well as the electrochemical cells and the uses thereof are also described.

Description

METHOD FOR RECYCLING GRAPHENE

ELECTRODE MATERIAL

PRIORITY REQUEST

The present application claims the priority, under the applicable law, of US Provisional Application No. 62 / 365,441 filed on July 22, 2016, the contents of which are hereby incorporated by reference in its entirety and for all purposes.

TECHNICAL AREA

The field of technology relates generally to methods for recycling graphene from electrode materials, for example, a method for recycling graphene from an electrode comprising graphene and an electrochemically active material used in Li-ion cells. The present technology also relates to the use of graphene thus recycled for the preparation of electrodes used in electrochemical cells.

STATE OF THE ART

Graphene is known to be an expensive material, and conventional methods for recycling graphene from Li-ion batteries use solvents such as N-methyl-2-pyrrolidone (NMP) to solubilize the binder (eg PVDF) and separate the graphene film of the current collector. This solubilization step is generally followed by a heat treatment (see Contestabile et al., J. Power Sources, 2001, 92, pages 65-69). Harmful solvents or strong acids or bases may also be used in these conventional methods. Also, industrial methods for recycling current collector materials, such as aluminum, are not efficient both economically and energetically (Gaines L, Sustainable Material and Technologies, 2001, 1-2, pp. 2-7).

There is therefore a need for novel methods for recycling graphene from an electrode material comprising graphene and an electrochemically active material, avoiding at least one of the disadvantages of the presently used methods. For example, such a new method would include simplified steps, use environmentally friendly solvents and / or involve lower energy consumption. SUMMARY

The present technology relates to a method for recycling an electrode material comprising graphene and an electrochemically active material, the method comprising the steps of:

(i) adding, in any order, water and a solvent immiscible with the electrode material, thereby forming a biphasic system comprising an organic phase and an aqueous phase;

(ii) separation of the organic and aqueous phases; and

(iii) filtration of the organic phase to recover graphene. In one embodiment, the method further comprises, prior to step (i), a step of washing the electrode material with a solvent to obtain a suspension of graphene and material. electrochemically active, and a filtration step of the suspension. For example, the washing step further comprises treating the suspension in an ultrasonic bath. The filtrate obtained during the filtration of the suspension may further comprise an additional step of washing with a solvent, for example, the same solvent as that used for the washing step.

In one embodiment, the method further comprises, prior to step (i), a heat treatment step performed at a temperature between about 400 ° C and about 550 ° C for at least 20 minutes, for example, at a temperature of about 500 ° C and for a period of time between 20 and 60 minutes. In another embodiment, the method further comprises a pre-drying step prior to the heat treatment step.

In another embodiment, the immiscible solvent used in the biphasic system of the process defined herein is a carbonate ester, for example, diethyl carbonate, dimethyl carbonate or ethyl methyl carbonate. In the biphasic system, the immiscible water / solvent ratio can range from about 3: 1 to about 1: 2, or from about 2: 1 to about 1: 1. After the separation of the two phases of the biphasic system, the organic phase is optionally washed with deionized water to remove residual traces of the electrochemically active material. The process also includes an optional step of recovering the aqueous phase and regenerating the electrochemically active material. In another embodiment, the electrochemically active material present in the electrode material is selected from ,2, 1-4 TiC, Li4TisOi2, Η2ΤΊ5Ο11, Η2ΤΊ4Ο9, or a combination thereof, LiM'PC in which M 'is Fe, Ni, Mn, Co, or a combination thereof, LiV ₃ 08 V2O5, LiMn ₂ 0 _4, UMO2, wherein M "is Mn, Co, Ni, or combinations thereof, Li (NiM"') 02, wherein M "is Mn, Co, Al, Fe, Cr, Ti, or Zr, and a combination thereof According to one example, the electrochemically active material present in the electrode material is a lithium titanate or a phosphate lithium and metal, for example, Li ₄ Ti ₂ O ₄ , LiFePO ₄ , or LiFePO ₄ coated with carbon.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic illustration of the method of recycling graphene-based electrodes according to one embodiment of the present technology.

Fig. 2 is a photograph showing the separation of graphene from an LTO powder according to one embodiment.

Figure 3 shows the thermogravimetric curves of a LiFePO ₄ / C (LFP) powder and a graphene powder (EG).

Figure 4 shows the thermogravimetric curves of a graphene powder before (EG) and after (EG recycled) application of the recycling method according to one embodiment.

Figure 5 shows the diffraction patterns of X-ray: a) a self-supporting layer of graphene, b) of a graphene layer recycled according to one embodiment on a Celgard ^® separator, c) a layer of oxide on a Celgard ^® separator, and d) a Celgard ^® separator alone. The peaks attributed to the oxide particles are identified by circles (·).

Figure 6 shows Scanning Electron Microscopy (SEM) images of the recycled graphene layer according to one embodiment and obtained at: a) 250X, b) 1000X, c) 5000X and d) 10000X. Circles may indicate residual oxide particles. Figure 7 shows SEM images of the oxide film deposited on a Celgard® separator, obtained at: a) 250X, b) 1000X, c) 5000X and d) 10000X. An optical photograph of the oxide film is also presented.

Figure 8 shows the specific charge capacities (squares) and discharges (circles) of a self-bearing graphene electrode cycled at rates ranging from 50 to 1000 mA / g.

Figure 9 shows the specific charge capacities (squares) and discharges (circles) of a recycled graphene anode, the anode being cycled at rates ranging from 50 to 1000 mA / g.

Figure 10 shows SEM images of a self-supporting graphene layer obtained at a) 250X, b) 1000X and c) 5000X.

Figure 11 shows charge / discharge profiles at rates ranging from 50 to 1000 mA / g for a graphene self-supporting electrode, where the second cycle is shown for each current density.

DETAILED DESCRIPTION In this document, the term "about" when followed by a measurement or reported value means within the acceptable limits of the experimental error as determined by the person skilled in the art, which will depend in part the way in which the value is measured or calculated, that is, according to the limits of the measuring equipment. This value will also take into account the number of significant digits expressed and the rounding of the values. In the alternative, unless otherwise indicated, when the term "about" is used in the present specification or claims, it means that a margin of error must be assumed, for example plus or minus 10 %, or plus or minus 5%, or plus or minus 1%, of the value described.

The use of graphene more widely is still limited by its high cost. Therefore, a recycling process to recover the graphene contained in a used battery has been developed. This method, an embodiment of which is illustrated in Figure 1, is simple, uses green solvents, avoiding the use of a large amount of NMP to solubilize the binder and separate the various components and materials of a battery. In addition, only a short heat treatment under ambient air may be required for particles of electrochemically active material coated with carbon.

According to a first aspect, this technology relates to a method for recycling an electrode material comprising graphene and, optionally, an electrochemically active material. The present method can be applied, for example, when the electrode material does not comprise a polymeric binder such as PVDF.

In one embodiment, the method includes a step of adding to the electrode material, in any order, water and an immiscible solvent. By "immiscible solvent" is meant here an organic solvent immiscible in water in the proportions and conditions of use (for example, at room temperature). The addition of water and immiscible solvent leads to the formation of a two-phase system comprising an organic phase and an aqueous phase. Graphene is then present in the organic phase, while the electrochemically active material is found in the aqueous phase. The immiscible solvent may be a carbonate ester such as diethyl carbonate, dimethyl carbonate or ethyl methyl carbonate. The solvent is used in proportions that allow the production of a biphasic system. For example, the two-phase system may contain water and the immiscible solvent in a ratio of from about 3: 1 to about 1: 2, inclusive. In a preferred embodiment, the solvent is dimethyl carbonate and the water / solvent ratio is from about 2: 1 to about 1: 1, or about 2: 1.

In one embodiment, the electrochemically active material comprises a material selected from the group consisting of titanates, lithium titanates, lithium and metal phosphates, vanadium oxides, lithium and metal oxides, and combinations thereof when relevant. For example, the electrochemically active material may be selected from ΤΊΟ2, Li ₂ TI03, Li ₄ Ti ₅ 0i2, H ₂ Ti ₅ 0n and H ₂ Ti ₄ 09 or a combination thereof, LiM'P0 wherein M 'is Fe , Ni, Mn, Co, or a combination thereof, LiV ₃ 0 ₈ , V ₂ O ₅ , LiMn ₂ 0 ₄ , LiM "O ₂ , wherein M" is Mn, Co, Ni, or a combination thereof, Li (NiM "') ₂ 0, wherein M" is Mn, Co, Al, Fe, Cr, Ti, or Zr, and combinations thereof. In one example, the electrochemically active material is selected from lithium titanates and lithium metal phosphates, for example, Li Ti50i2 or LiFePC.

The recycling process may comprise a step of separating the organic phase from the aqueous phase. Graphene is therefore recovered from the material of the electrode using a liquid-liquid extraction. The organic phase comprising graphene may also be washed with deionized water to remove the remaining traces of the electrochemically active material. The organic phase thus obtained is then filtered to recover graphene. The graphene recovered by the present recycling method can then be used in the manufacture of electrode materials. The aqueous phase can also be recovered and the electrochemically active material can be regenerated for possible use in the manufacture of electrode materials.

Particles of electrochemically active material present in the electrode material to be recycled may also be coated with carbon. For example, the electrochemically active material may be a carbon-coated lithium-metal phosphate (LiM'PC as described herein), such as carbon-coated LiFePC (referred to below as LiFePO / C). In the case where the electrochemically active material is coated with carbon, the method of recycling graphene from the electrode material may comprise additional steps before the addition of water and an immiscible solvent (biphasic treatment). In one embodiment, the method comprises a step of washing the electrode material with a solvent, thereby recovering a mixture of graphene and electrochemically active material. The solvent may be a carbonate ester such as diethyl carbonate, dimethyl carbonate or ethyl and methyl carbonate. For example, the electrode material may be mixed with the solvent and treated in an ultrasonic bath.

In one embodiment, the mixture comprising graphene and the electrochemically active material resulting from the previous washing step is filtered to remove the solvent and recover a powder comprising graphene and the electrochemically active material. The filtered powder may also be washed with a solvent to remove excess salt or any other soluble impurities. The solvent may be the same solvent used in the previous washing step, or any other suitable solvent known to those skilled in the art. According to one embodiment, the powder is then heat-treated. The heat treatment can be carried out at a temperature of between about 400 ° C and about 550 ° C inclusive, and last for at least 20 minutes. For example, the temperature of the heat treatment is about 500 ° C. The heat treatment can last between 20 to 60 minutes. Such a heat treatment makes it possible to remove the coating of particles of electrochemically active material coated with carbon and / or allows the oxidation of the electrochemically active material.

In one embodiment, a pre-drying step can be performed before treating the powder thermally. For example, the graphene powder and electrochemically active material may be pre-dried by air blast or by any other common technique.

In one embodiment, the step of adding water and an immiscible solvent to the graphene powder and electrochemically active material, and the step of separating and filtering the organic phase, as described herein. above, are performed after the heat treatment step.

EXAMPLES

The following non-limiting examples are illustrative embodiments and should not be construed as limiting the scope of the present invention. These examples will be better understood with reference to the accompanying figures. Example 1 Electrode Preparation and Electrochemical Cell Based on Graphene a) Electrochemical Exfoliation of a Graphite Sheet

Graphene powder was obtained by electrochemical exfoliation of graphite foil (Alfa Aesar, 7.5 cm ^χ 2 ^χ cm 0.05 cm) (see Canadian Patent Application No. 2,803,772). For example, the graphite sheet is used as anode (connected to the positive terminal of a DC power supply). The counter electrode is then made of a platinum lattice (4 cm ² ). The graphite sheet and the counter-electrode are immersed in an electrolytic solution of 0.1 M H 2 SO 4 and are separated by a constant distance of 4 cm. The electrochemical exfoliation was performed by applying a DC voltage of 6, 8 or 10 V between the two electrodes. After about 1 h of electrolysis, the solution containing the exfoliated graphene was filtered under vacuum with an assembly of Buchner type and a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 0.47 μηι. The resulting powder exfoliated graphene named EG in the Figures of the present specification, was then washed several times with water Nanopure ^® to remove residual acid before being dispersed in dimethylformamide (DMF) by ultrasonication for 10 min. The dispersion was collected and the resulting material was treated for 1 hour at 1000 ° C under 5% hydrogenated argon and then used for anode and cathode fabrication as described below. b) Preparation of graphene self-supporting electrodes For the preparation of graphene self-supporting electrodes, a measured quantity of the exfoliated graphene powder of step a), chosen so as to reach a concentration of between 100 and 400 mg / L was dispersed in 50 ml DMF and placed in an ultrasonic bath for 30 minutes. Regular (or "fresh") and recycled graphenes were both used. The resulting mixture was then filtered through a nylon ^® filter for several hours. When sufficiently dry the graphene layer was removed from the filter and dried again at 80 ° C under vacuum for 24 h. The graphene layer was then heat-treated in a tubular furnace at 1000 ° C for 2 h under 5% hydrogenated argon, and used as an electrode without additive, binder or current collector. c) Preparation of electrochemical cells

The different graphene electrodes were characterized in cell button type two-electrode with lithium metal as a negative electrode, a Celgard ^® -2320 separator impregnated with an electrolyte of 1M LiPF6 in a mixture of ethylene carbonate (EC ) / diethyl carbonate (DEC) / dimethyl carbonate (DMC) (1: 1: 1 per vol.) and exfoliated graphene or 100% recycled exfoliated graphene as a positive electrode. The cells were assembled in a glove box filled with dry argon. The cells were monitored with a VMP3 ™ potentiostat and the cycling charge / discharge procedure was performed in galvanostatic mode between 0.01 and 1.5 V against Li / Li ⁺ at different current densities, after 1 Open circuit power-off time (OCV). For each current density ranging from 50 mA / g to 1 A / g, 10 cycles were recorded. Example 2 - Recycling of Li-ion batteries and graphene recovery a) Recycling of Graphene / LFP electrodes

As illustrated in FIG. 1, the LFP electrodes comprising graphene and electrochemically active material (LFPcelgard) were made according to the method of Example 1 where no binder or current collector was used, and where electrode materials comprising graphene and electrochemically active material have been filtered on a polymeric separator to form a layer of electrode material acting as an electrode. Graphene and the electrochemically active material (LiFePCVC), used in a graphene / LiFePC ratio of 20:80, were recovered by washing the various components with dimethyl carbonate (DMC) in an ultrasonic bath. The mixture was filtered and washed again with DMC to remove excess salt. After a short pre-drying, the resulting powder, consisting of LiFePO / C and graphene, was heat-treated at 500 ° C for 30 min to remove the carbon coating and to oxidize the LiFePO particles. After this step, graphene was separated from the oxidation and degradation products of LiFePO / C by dispersion in a water / DMC mixture (volume ratio of 2: 1). The organic phase contained the majority of graphene. The aqueous phase (on top) was orange, which confirmed the presence of oxidized species such as Li3Fe2 (P0) 3 and Fe2O3. Then, the organic phase was separated and washed twice with deionized water to remove residual traces of oxidized products. Finally, the DMC phase was filtered and the recycled graphene powder was obtained in a yield of about 80%. b) Graphene / LTO Electrode Recycling

The active material particles of LTO present in the electrode material were not previously coated with a carbon layer. Therefore, as illustrated in the image of Figure 2, no heat treatment was necessary. The electrochemically active material (Li ₄ Ti ₅ O 12 and graphene) was therefore dispersed in DMC, filtered and washed with DMC to remove the remaining lithium salts. The resulting powder was then suspended in deionized water and DMC. More specifically, LTO (present in the aqueous phase) was separated from graphene (present in the organic phase). The organic phase was washed twice with deionized water, to obtain an organic phase rich in graphene and an aqueous phase containing LTO. The phases were separated and the graphene powder was isolated by filtration.

Example 3 - Characterization of electrodes and graphene material a) Thermogravimetric analysis The thermal stability of regular graphene and recycled graphene powders was evaluated by thermogravimetric analysis (TGA) carried out under a constant air flow rate of 90 ml / min. at a temperature of 30 to 1000 ° C and a heating rate of 10 ° C / min, using TGA (Q500 ™) / Discovery MS ™ instruments.

The thermogravimetric curves of the LiFePOVC and graphene powders are shown in Figure 3. Some notable differences are observed between the two materials above 300 ° C. First, the graphene remained stable until about 550 ° C, at which temperature the onset of combustion was observed. On the other hand, a weight gain of about 2.3% was observed between 300 and 400 ° C for the LiFePOVC powder. It is possible that this weight gain is the result of the oxidation of LiFePOVC to form Li3Fe2 (P0) 3 and Fe2C> 3, this oxidation being also accompanied by the degradation of the carbon coating (Belharouak et al. , Electrochem Commun, 2005, 7, 983-988, Hamelet et al., J. Mater Chem, 2009, 19, 3979-3991). A temperature of 500 ° C was therefore selected for the heat treatment in Example 2 of the mixture of graphene and LiFePOVC recovered after a first washing step. The oxidation products of LiFePOVC were then separated from the graphene sheets in a subsequent step. A yield of about 80% was obtained according to the weight of graphene used in the different batteries and the weight of graphene recovered at the end of the process.

To validate the efficiency of the recycling process, the recycled graphene powder has also been characterized by thermogravimetric analysis. Figure 4 shows the thermogravimetric curves for the graphene powder front (curved identified "EG" in Figure 4) and after recycling (curved identified "EG recycled" in Figure 4). It appears that the two curves are similar and the only difference observed is that the beginning of the combustion of recycled graphene powder occurs at a slightly lower temperature (about 25 ° C lower) compared to fresh graphene. This behavior could be explained by a difference in the size of the graphene sheets. Indeed, Additional heat and ultrasound treatments may have led to a powder composed of smaller particles of recycled graphene. b) X-ray diffraction analysis

LFP electrode graphene was recovered by the present recycling process, and a thin oxide film was also obtained. The films of oxide, regular graphene and recycled graphene were characterized by X-ray diffraction (XRD) using a Philips X'Pert ™ diff-2Θ diffractometer with Cu Και radiation, α ₂ (λι = 1.5405Â, λ ₂ = 1.5443) and a monochromator to avoid the presence of radiation Κβ. Both films were deposited on a monocrystalline Si (400) plate (single peak at 2Θ = 69). Data was collected between 5 ° and 60 ° using increments of 0.02 ° and an integration time of 1.3 sec increments with an X'Celerator ™ detector.

A 100% recycled graphene layer was formed on a Celgard ^® separator. An oxide layer was also prepared on a Celgard ^® separator by filtration of the aqueous solution containing the oxidized species. These layers of graphene and oxide have been characterized by X-ray diffraction (XRD), as shown in Figure 5.

The XRD diagrams of a self-supporting graphene layer and a Celgard ^® separator alone are also shown in Figure 5. Figure 5a shows an asymmetric net peak around 2Θ = 27 ° for the graphene free-standing layer, which was assigned to the plane (002) of a graphitic material. In addition, a low intensity peak at about 2Θ = 55 °, generally observed for graphene powders, is also present (Yuqin et al., J. Power Sources, 1997, 68, 187-190). Finally, the peak flared at about 2θ = 10-15 ° is assigned to a graphite oxide material generated during the electrochemical exfoliation of a graphite sheet (Vargas et al., Electrochim Acta, 2015, 165, 365 371, Wang et al., J. Phys Chem, 2008, 112, 8192-8195, Guo et al., ACS nano, 2009, 3, 2653-2659).

In Figure 5d, the XRD chart of the Celgard ^® separator alone shows five peaks between 12 and 27 °. For the oxide film, in addition to the five peaks of the Celgard ^® support, several small peaks were observed between 20 and 27 ° and identified by circles in Figure 5c. For recycled graphene layer (Figure 5b), the XRD pattern is consistent with the presence of Celgard ^® and graphene and the absence of oxides. These results confirm the effectiveness of the recycling process as described here. c) Scanning electron microscopy

Morphological studies of different electrode films were performed using a JEOL JSM-7600F ™ scanning electron microscope equipped with an Oxford Instruments X-Max 80 ™ EDS detector. The recycled graphene layer has also been characterized by scanning electron microscopy (SEM). The SEM images are shown in Figure 6 with different magnifications. For comparison purposes, the SEM images of a free-standing layer with fresh graphene are also shown in Figure 10, and show an assembly of graphene sheets of several microns. The texture and size of the recycled graphene leaflets are different from what was observed for a free-standing graphene film shown in Figure 10. This result is also in agreement with the thermogravimetric analysis which demonstrated a slightly lower temperature. of combustion for recycled graphene powder. This result corroborates the hypothesis that this effect may be due to a difference in size of the graphene sheets resulting from the additional thermal and ultrasonic treatments. In addition, there is no clear evidence of the presence of residual oxide particles in the film. Tiny and irregular particles, identified by circles in Figure 6, have been observed but can not be attributed to the presence of oxide.

The oxide layer has also been characterized by scanning electron microscopy. Figure 7 shows SEM images at different magnifications. Although not shown here in black and white, the image of the inset separator of Figure 7a shows an orange color for the filtered powder, suggesting that the LiFePO / C material was completely oxidized during the heat treatment. at 500 ° C. These observations show that the steps of separation and washing with deionized water, described in Figure 1, allowed efficient separation of graphene from the oxide powder.

Example 4 Electrochemical Performance of Electrodes Comprising Exfoliated Graphene and Recycled Exfoliated Graphene

The electrochemical performances of graphene free-standing electrodes were evaluated in button cells with lithium metal as a counter-electrode. The regular graphene powder (fresh) was also used to prepare a self-supporting film graphene, which was used as an electrode in a Li-ion battery without adding a current collector, binder or carbon additive. The specific charge and discharge capabilities of a graphene free-standing electrode are shown in Figure 8. A discharge capacity of approximately 250-275 mAh / g was obtained for applied currents between 50 and 200 mA / g. Capacity decreased continuously when the cycling rate was increased. At high rate, the discharge capacity appeared to stabilize and an average capacity of 85 mAh / g was obtained at 1A / g.

Figure 11 illustrates the charge and discharge profiles of the self-supporting graphene electrode cycled at different current densities ranging from 50 to 1000 mA / g. The curves display the voltage profiles typically observed for graphite electrodes (Endo et al., Carbon, 2000, 38, 183-197). At low current densities (between 50 and 200 mA / g), the curves were very similar with no significant increase in polarization. The charging voltage increased considerably with the increase of the cycling rate due to the higher resistance and polarization. As a result, the specific capacities recovered for high charge and discharge currents were smaller.

An electrode prepared with recycled graphene obtained by the recycling method as defined herein has also been tested in a button cell. The specific charging and discharging capabilities of the recycled graphene electrode film are shown in Figure 9. The electrochemical performance was similar to that obtained for the graphene self-supporting electrode shown in Figure 8. Interestingly, the irreversible capacitance during first charge / discharge cycle was smaller after recycling, presumably due to additional heat treatments and also different particle morphology (Zheng et al., J. Electrochem Soc, 1999, 146, 4014-4018). In addition, current densities greater than 200 mA / g gave slightly higher specific capacities after recycling. This improvement could be explained by the smaller graphene sheets after recycling, which would facilitate the storage of lithium at high current densities.

When prepared by the method of Example 1, the electrodes comprising graphene for use in Li-ion batteries were produced without a current collector, binder or harmful solvents normally used to prepare the electrode compositions. A graphene powder, obtained by electrochemical exfoliation of a graphite sheet, has was used as an additive to an active material (LiFePC / C or LUTisO ^) for the manufacture of Li-ion battery electrodes.

The electrode material comprising graphene and an electrochemically active material was then recycled to recover graphene by the method described herein. One of the main advantages of this fast green process is that NMP and / or strong acid / base treatments are not needed to recover the transition metals or graphene. Only a carbonate ester solvent (such as dimethyl carbonate) and water can be used for the washing and separating steps. An aqueous phase containing the electrochemically active material or its oxidized version is obtained and can be processed to regenerate the electrochemically active material for subsequent use in the manufacture of batteries. In addition, the recycled graphene powder is isolated with a yield of at least 80%. This yield could be further optimized. Recovered graphene can also be used later for the manufacture of new batteries. A simple and low-energy recycling method has therefore been developed to reuse the graphene present in used lithium or lithium-ion batteries.

When the electrochemically active material is not coated with carbon, the heat treatment is avoided, considerably reducing the costs of the process. Finally, with the present simple and environmentally friendly method, a graphene powder can be recovered as well as the active electrode material, and possibly reused in the manufacture of composite electrodes.

The performance of the recycled graphene electrode has also been demonstrated to be at least similar to that of the film made with electrochemically exfoliated graphene. These results have also shown that the recycling of graphene by the present method makes it possible to recover the majority of graphene from the electrode, as well as the preservation of the electrochemical properties of graphene. This could promote the use of graphene in Li-ion batteries.

Many modifications could be made to any of the embodiments described above without departing from the scope of the present invention. All references, patents or scientific literature referred to herein are incorporated herein by reference in their entirety for all purposes.

Claims

A method for recycling an electrode material comprising graphene and an electrochemically active material, the method comprising the steps of:

(i) adding, in any order, water and a solvent immiscible with the electrode material, thereby forming a biphasic system comprising an organic phase and an aqueous phase; and

(ii) separating the organic phase and the aqueous phase; and

(iii) filtering the organic phase to recover graphene.

2. The process of claim 1, wherein the immiscible solvent is a carbonate ester.

3. The process of claim 2, wherein the carbonate ester is diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate or a mixture of at least two thereof.

The process of any one of claims 1 to 3, wherein the biphasic system has a water / solvent ratio of from about 3: 1 to about 1: 2.

The process of any one of claims 1 to 4 wherein step (ii) further comprises washing the organic phase with deionized water prior to step (iii) of filtration to remove residual traces of electrochemically active material.

The method of any one of claims 1 to 5, the method further comprising, prior to step (i), steps of washing the electrode material with a solvent to obtain a suspension of graphene and electrochemically active material, and filtration of said suspension.

The method of claim 6, wherein the washing step further comprises treating the suspension in an ultrasonic bath.

The process of claim 6 or 7, further comprising an additional step of washing with a solvent after the filtration step.

The process of any one of claims 1 to 8, further comprising, prior to step (i), a heat treatment step performed at a temperature of from about 400 ° C to about 550 ° C for at least 20 minutes.

The process of claim 9, wherein the heat treatment is conducted at a temperature of about 500 ° C and for a period of time between 20 and 60 minutes.

The process of claim 9 or 10, further comprising a pre-drying step prior to the heat treatment step.

The process of any one of claims 1 to 11, wherein the electrochemically active material is selected from ΤΊΟ2, Li2i10, LiTisOi2, Η2ΤΊ5Ο11 and HbTUOg, or a combination thereof, LiM'PC wherein M 'is Fe , Ni, Mn, Co, or a combination thereof, UV3O8, V2O5, LiMn20, LiM "C> 2, wherein M" is Mn, Co, Ni, or a combination thereof, Li (NiM ") C> 2, wherein M "is Mn, Co, Al, Fe, Cr, Ti, or Zr, and combinations thereof.

The process of any one of claims 1 to 11, wherein the electrochemically active material is lithium titanate or lithium metal phosphate.

The process of claim 13, wherein the electrochemically active material is carbon-bonded Li TisO 12, LiFePO, or LiFePO.

The process of any one of claims 1 to 14, further comprising steps of separating the aqueous phase and regenerating the electrochemically active material.